This application claims the priority of German application 197 32 056.2, filed Jul. 25, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a vacuum system, particularly for a transfer system having vacuum grippers.
Transfer systems, particularly transfer systems for large-part presses in which relatively large sheet metal parts are to be placed in press stations and are to be moved therefrom, frequently have vacuum grippers which temporarily hold the sheet metal parts. The vacuum grippers must be supplied with a vacuum which in practice is usually provided by venturi nozzles acting as fluid entrainment pumps. These are operated by compressed air taken from a compressed-air supply system. As soon as the fluid entrainment pump is acted upon by compressed air serving as a pump fluid, it generates a vacuum at its suction connection which is guided to the vacuum grippers. In order to switch the vacuum on and off, the compressed air guided to the fluid entrainment pumps is switched on and off by way of a corresponding valve device. The valve device is controlled by an electric control unit which is connected by a corresponding number of control lines with the valve device.
While, during the buildup of the vacuum, the fluid entrainment pump must remove relative large amounts of air from the vacuum grippers and the connected pipes, the suctioned and held sheet metal parts will then block the admission of air so that the vacuum must only be maintained but hardly any more air must be conveyed. The compressed-air quantity used for the operation of the fluid entrainment pumps must be generated by the compressed-air system of the transfer system or the press system. A corresponding dimensioning is required here, in which case naturally a low compressed-air consumption is desirable.